Agriculture bearings are strongly stressed machine components parts of which feature high accuracy. To be able to utilise fully functional properties of bearings and avoid damaging them before the end of their service life, assembly and potentially disassembly procedures have to be correctly specified. To do so, the structure of location has to be well known, suitable workplace and assembly tools made available to simplify the assembly and disassembly of bearings. It is very important that the assembly is performed by workers who are properly qualified and equipped with protective equipment.
Worksite must be equipped with suitable assembly tools and jigs to make the work comfortable and also safe. Equipment varies by the type and size of bearings to be assembled at the worksite. Very important is to make sure that these tools are clean and the work is performed in a clean working environment. In negative sense, impurities have decisive impact on the run of bearing when it is in service. Depending on the size and origin of impurities they may cause increased noise level of bearing and may also cause a bearing failure. The same conditions of cleanliness have to be applied in the preparation of all lubricating agents and components associated with location. Assembly worksite has to be therefore separated from normal production and only reserved for assembly of bearings. The worksite must be sufficiently spacious, dry and dust-free. No adjustments of components are supposed to be performed there, such as polishing, drilling or welding that could cause impurities to penetrate into the location area, or no air compressing devices shall be used in the proximity. The worksite shall not be exposed to weather effect since bearings are very sensitive to humidity, especially after being washed off preservative agents or old lubricant.
Prior to the commencement of every assembly the work procedure has to be specified based on drawing documentation to define individual work steps. In special cases that differ from common practice, detailed assembly instructions have to provided, containing all assembly details, such as specification of needed work tools and equipment for assembly and disassembly, measuring instruments, special tooling, way of heating the bearings up, type and amount of lubrication, etc.
Preparation of bearings for assembly
Prior to the assembly, the fitter has to make sure whether the designation stated on the bearing corresponds with that on the bearing packaging stated on the drawing.. In order to maintain cleanliness, bearings are taken out of the packaging just before the assembly. Only in exceptional cases the bearing is cleared of preservative agent. Damaged packaging indicated potential contamination of bearings during the storage; so the bearings always have to be washed out prior to the assembly.
Bearings are washed out in a clean suitable tank using a brush or a fibre-free cloth. During the washout one of the bearing races have to be rotated with. If one bath is not sufficient to wash out the bearing, multiple baths are used depending on the level of contamination. After the washout, the bearing has to be provided with protective oil or grease layer depending on the type of lubrication to be used in run. During preservation, one race of the bearing is slowly rotated with so that the orbits of both races as well as the surface of rolling bodies come to contact with the preservative agent.
After preservation, the bearing has to be protected from contamination and mounted to respective place as soon as possible. No additional mechanical adjustment shall be done on roller bearings, such as making holes for supply of lubricant, slots, recesses, etc., since this might release tension in the races that would cause early damage to the bearing. Besides that, there is a risk that the bearing can be contaminated with splinters or abrasion dust.
When handling bearings one needs to use gloves and lifting equipment to simplify the operation and enhance work safety. I
Preparation of location components for assembly
Prior to the assembly, all located parts must be thoroughly clean and cleared of burrs caused during their machining. Unmachined surfaces of the inside of rolling location bodies must be perfectly clean and cleared of the moulding sand residues, and provided with a protective coating. Also, all lubrication holes and threads have to be cleared thoroughly. All sharp edges need to be bevelled.
Prior to the assembly itself you need to check that the defined tolerances, geometrical accuracy and quality of bearing saddle surface and that in the body have been met. The accuracy of rolling bodies’ dimensions need not checked prior to the assembly.
To ensure reliable operation of bearings, bearings must not be mounted on shafts which do not guarantee the accuracy of geometrical shape, on bended shafts or on shafts with mechanical damage. Therefore the shaft has to be checked carefully prior to the assembly
Assembly of bearings with cylindrical bore
Different types and sizes of roller bearings require different assembly procedure. In principle, direct hammer strokes on the race (ring) collars, on cages or rolling bodies have to be avoided during the assembly. When assembling non-separable bearings, the mounting force must act on the race located with overlap that is mounted as first. In no case shall the mounting force be transferred via the rolling bodies of the bearings. Thus the bearing is firstly mounted on journal by loading via the inner race and then the entire bearing is pushed in the body where the location is usually sliding
Assembly of bearings with tapered bore
Bearings with tapered hole (bore) are mounted on shaft by means of clamp or dismantling sleeves, or alternatively directly on tapered journal. Inner race with tapered bore is always placed on the journal firmer than a race with cylindrical bore. Fixed location is achieved either by pressing the inner race on by means of a nut or a tapered sleeve. In both cases the inner race will expand and cause reduction of radial clearance in the bearing. Therefore a method has to be determined that would correctly specify the overlap. This can be achieved by measuring the radial clearance reduction using a feeler gauge. The clearance before and after assembly must be measured between the inner race and unloaded rolling body. This method suits to medium size and big spherical-roller bearings. Other methods are e.g. measuring of the lock nut torque angle or measuring of axial displacement of the inner race on the tapered journal. In the assembly of double row tilting ball bearings, the clamp bushing nut can be tightened to such extent that the inner ring can be smoothly turned and tilted. The assembly method should be consulted with the manufacturer.
Reliability of fixation of spherical-roller bearings can be checked by measuring of axial displacement of the inner race on the journal or tapered sleeve. The initial position for measuring of this displacement will be achieved when the contact surfaces (of the race, sleeve, shaft) abut against each other on the entire bearing surface.
Bigger bearings require much bigger mounting force, and that’s why hydraulic nut or pressure oil method should be applied in their assembly, when oil is brought between the contact surfaces of the race and journal under high pressure This creates an oil film that reduces friction between the bearing surfaces. This method can be used also for the assembly onto clamp bushings or dismantling sleeves that are modified to suit this method.
Storage of bearings
JB bearings are stored and packed in a way that maintains the properties of the bearings as long as possible. The prerequisite for achieving these goals is achieving the conditions for storage of bearings and handling them.
Relative air humidity in the storage should not exceed 60%, and there should be no major temperature oscillations. Most convenient temperature range for storage of bearing is between 15 and 25ºC.
Bearings should not be exposed to vibrations and shocks. When stored, bearings must not be exposed to aggressive media, such as gases, fog or aerosols of acids, lyes and salts. Also the effect of direct sunlight has to be prevented since it may cause major temperature oscillations in the container. Big bearings, especially those of light series, must not be stored as standing. They should be placed horizontally to avoid deformation of races (rings). Bearings must not be stored in racks made of fresh timber or on a stone floor. Bearings must not be placed in the proximity of heating or water piping.